1. Field of the Invention
The present invention relates to a modem, in particular to a modem adaptive for a data recording and reproducing system provided in a data communication system such as in a telephone service.
It is noted that a modem is a combination of a modulator and a demodulator at each end of a telephone line to convert binary digital data to audio tone signals suitable for transmission over the line, and vice versa, which is also known as data-set.
2. Description of the Related Art
It is a common practice to provide a modem in a data communication equipment such as a facsimile system for data transmission via wire or radio communication lines. On the other hand, there has been developed LSI (large scale integration) for recording and reproduction of data, which is employed in a data communication system such as a caretaker telephone system for recording and reproducing audio tone or sound data. In recent years, in a facsimile system there is accommodated LSI for recording and reproducing audio tone data for transmission of the data.
FIG. 1 shows a schematic construction of a conventional facsimile system F having such an audio tone data recording and reproducing faculty using a modem and LSI. In such a conventional facsimile system, as shown in FIG. 1, there is provided a line control unit (referred to as LCU hereinafter) 11 having telephone lines 10 and 10' connected thereto, and telephone equipment 12 is connected to the LCU 11 through the telephone line 10'. The LCU 11 is connected to a data recording and reproducing LSI 20 for recording and reproducing audio tone data through a bus line and is also connected to a modem 30 through another bus line.
In the modem 30, there are accommodated analogue-to-digital (referred to as A/D hereinafter) and digital-to-analogue (referred to as D/A hereinafter) converters 30a and 30b. When picture data signals of analogue form are transmitted to the facsimile through the telephone line 10, the received analogue data signals of the picture data are A/D converted through the A/D converter 30a, thereafter the digital picture data are demodulated in the modem 30 and the demodulated digital data are transmitted to a data bus 13. The data bus 13 has a microprocessor 14, a memory unit 15 and a picture reading and recording unit 16 connected thereto. The digital picture data outputted onto the bus 13 from the modem 30 are temporarily stored in the memory unit 15 under the control of the microprocessor 14. Subsequently, the picture data stored in the memory unit 15 are sequentially read out to be transmitted to the picture reading and recording unit 16 in which the picture data are recorded. On the contrary, when picture data are transmitted from the facsimile used as transmitting equipment, the digital picture data recorded in the picture reading and recording unit 16 are read out onto the bus 13 and temporarily stored in the memory unit 15. Subsequently, the digital picture data stored in the memory unit 15 are sequentially read out and transmitted to the modem 30 through the bus line 13. The digital picture data are modulated in the modem 30 into data signals suitable for the transmission of the picture data, thereafter the modulated digital picture data are D/A converted through the D/A converter 30b. The analogue picture data outputted from the D/A converter 30b are transmitted onto the telephone line 10 via the LCU 11.
Also in the LSI 20 for recording and reproducing audio tone data, there are provided A/D and D/A converters 20a and 20b. When audio tone data signals of analogue form are transmitted from the telephone equipment 12 to the facsimile through the telephone line 10', the input analogue data signals are applied to the A/D converter 20a of the LSI 20 through the LCU 11 and A/D converted through the A/D converter 20a. The A/D converted signals are coded in the LSI 20. The coded digital audio tone data signals are outputted from the LSI 20 onto the bus line 13 and stored in the memory unit 15 under the control of the microprocessor 14. The digital audio tone data stored in the memory unit 15 are read out and transmitted to the LSI 20 under the control of the microprocessor 14 when required. The digital audio tone data applied to the LSI 20 from the memory unit 15 are decoded in the LSI 20 and D/A converted through the D/A converter 20b, thereby recovering the original analogue audio tone data. Subsequently, the D/A converted audio tone data signals are outputted from the D/A converter 20b and transmitted onto the telephone line 10 or to the telephone equipment 12 for hearing through the LCU 11.
As described above, in the conventional data communication equipment such as a facsimile, when an audio tone data recording and reproducing function is provided in addition to the picture data communication function in the data communication equipment, it is required to provide the LSI 20 for recording and reproducing the audio tone data in addition to the modem 30. That is to say, it is required to provide a modem 30 an and LSI 20 individually having a pair of A/D and D/A converters respectively in the data communication equipment. Accordingly, it becomes difficult to reduce the size and cost of the equipment.